The present invention relates to a balance shaft having a gear for a piston engine, having a bearing journal, a gear section, and an unbalanced section.
In modern piston engines, balance shafts are used in order to compensate for occurring vibrations and imbalances of the engine. The free mass forces and free mass torques which occur in single cylinder piston engines or in multi-cylinder piston engines are reduced or compensated for by the balance shafts.
It is typical to implement these balance shafts as forged parts. The forged parts are semifinished shafts on which the gears for driving the balance shaft are forged, so that they are connected to the balance shafts. Alternatively, the gears can also be connected in a rotation-locked manner to the balance shaft via press fits or other shaft-hub-connections. This is also true for unbalanced masses on the balance shafts. These can also either be forged on or fastened on via press fits. In some embodiments, the unbalanced masses are also fastened using machine elements. Welding the unbalanced masses on the balance shafts is also known.
In the prior art, the bearing journal and the gearings, i.e., the gears of the shaft, are hardened. In some cases, the entire shaft is also case hardened, nitrided, or nitrocarburized. In most of the cases, the heat treatment is performed as induction hardening. The gears of the balance shaft are always hardened in the case of forged balance shafts.
Balance shafts made of cast iron are also known, on which gears made of steel are shrink-fitted. The bearing journals of these balance shafts are optionally inductively hardened. The gears made of steel are typically case hardened. In some cases the gear is inductively hardened.
Furthermore, the currently predominantly practiced mounting of the balance shafts in friction bearings is increasingly being either completely or partially replaced by roller mounting for the purpose of reducing internal-engine friction losses. Roller mounting of the balance shafts is implemented both in the balance shaft housings and also directly in the cylinder crankcase.